1、INTERNATIONAL STANDARD lSO/IEC 14478-4 First edition 1998-12-15 Information technology - Computer graphics and image processing - Presentation Environment for Multimedia Objects (PREMO) - Part 4: Modelling, rendering and interaction component Technologies de /information - lnfographie et traitement
2、dimages - Environnement de prksentation dobjets multimedia (PREMO) - Partie 4: Composant pour la mod b) within the primitive hierarchy, specific provision for describing the temporal structure of multimedia data through the stepwise construction of structured primitives from component data; c) provi
3、sion of abstract types for modellers. renderers and other supporting devices, enabling the integration of such devices or any future subtypes representing real software or hardware, into a processing network of such devices; d) provision of an object type to map synchronization requirements expresse
4、d within multimedia primitives into control of the stream and synchronization mechanisms provided by ISO/IEC 14478-2 and ISO/IEC 14478-3. The Modelling, Rendering and Interaction Component relies on the object types and services defined in PREMO Part 2: Foun- dation Components (ISO/IEC 14478.2), and
5、 PREMO Part 3: Multimedia Systems Services (ISO/IEC 14478-3). 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO/IEC 14478. At the time of publication, the editions indicated were valid. All standards are
6、 subject to revision, and parties to agree- ments based on this part of ISO/IEC 14478 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. ISO/IEC I 1
7、072: 1992, lrlformation technology - Computer graphics - Computer Graphics Reference Model (CGRM). ISO/IEC 7942-l : 1994, Information technology - Computer graphics and image processing - Graphical Kernal System (GKS) - Part I: Functional description. ISOIIEC 9592: 1997, Information technology - Com
8、puter graphics and image processing - Programmers Hierarchical Inter- active Graphics System (PHIGS). 1 ISOHEC 14478-4:1998(E) 0 ISO/IEC ISOIIEC l4478- I : 1998, Information technology - Computer graphics and image processing - Presentation Environment for Multimedia Objects (PREMO) - Part I: Fundam
9、entals of PREMO ISOIIEC 14478-2: 1998, Information technology - Computer graphics and image processing - Presentation Environment for Multimedia Objects (PREMO) - Part 2: Foundation component ISOlIEC 14478-3: 1998, Information technology - Computer graphics and image processing - Presentation Enviro
10、nment for Multimedia Objects (PREMO) - Part 3: Multimedia systems services 3 Definitions 3.1 PREMO Part 1 definitions This part of ISO/IEC 14478 makes use of all terms defined in ISO/IEC 14478-I (Fundamentals of PREMO). 3.2 PREMO Part 2 definitions This part of ISO/IEC 14478 makes use of all terms d
11、efined in ISO/IEC 14478-2 (Foundation component). 3.3 PREMO Part 3 definitions This part of ISO/IEC 14478 makes use of all terms defined in ISO/IEC 14478-3 (Multimedia systems services component). 3.4 Additional Definitions For the purposes of this part of ISO/IEC 14478, the following definitions ap
12、ply. 3.2.1 modellet-: a virtual device that produces primitives on at least one output port. 3.2.2 renderer: a device that accepts primitives on at least one of its input ports. 3.2.3 media engine: a virtual device that accepts primitives from at least one of its input ports, and produces primitives
13、 on at least one of its output ports. 3.2.4 presentation: a collection of primitives that can be perceived by the operator. 3.2.5 coordinate: a primitive used to define a location in an nD space. 3.2.6 primitive: a structure describing information to be rendered, or information received through inte
14、raction. 3.2.6.1 form primitive: a primitive whose presentation has to be constructed by a renderer from an explicit description in terms of aspects or properties that characterize a class of perceivable representations. 3.2.6.1.1 geometric primitive: a form primitive used to define a shape or exten
15、t within nD space. 3.2.6.2 captured primitive: a primitive for which some or all of the perceivable aspects of the primitive have been en- coded in some format defined externally to the PREMO standard. 3.2.6.3 structured primitive: a primitive that contains a collection of other primitives. 3.2.6.4
16、modifier primitive: a primitive that describes a change to the presentation of another primitive. 3.2.6.4.1 acoustic modifier: a modifier that changes properties of the sound generated by other primitives. 3.2.6.4.2 structural modifier: a modifier that affects the spatial and/or temporal aspects of
17、another primitive. 3.2.6.4.3 visual modifier: a modifier that affects the (non structural) visual appearance of a primitive. 2 0 ISO/IEC ISO/IEC 1447%4:1998(E) 3.2.6.5 wrapper primitive: a primitive that carries a value drawn from some PREMO non-object data type. 3.2.6.6 tracer primitive: a primitiv
18、e that carries an event for use in monitoring and coordinating the transfer of media data across a network. 3.2.7 input device: a device used to obtain data from the operator. 3.2.8 graphics: the construction, manipulation, analysis and presentation of pictorial representations. 3.2.9 scene: a devic
19、e for storing and controlling access to a collection of primitive structures. 3.2.10 primitive structure: a collection of primitives organized into a structure that represents some or all of the data that describes a multimedia presentation. 3.2.11 coordinator: a MRI device that can manipulate the s
20、treams connecting its components. 3.2.12 router: a device for controlling the flow of data between streams connected to its ports. 3.2.13 temporal extent: the duration in time allocated or used for the presentation of some primitive. 3.2.14 operator: the external object that sends or receives inform
21、ation through a virtual device interface. 3.2.15 application: the external object or client that uses a PREMO system by creating objects, invoking operations on ob- jects, and using types defined by PREMO. Applications are not modelled in the PREMO system, but their interactions with a PREMO system
22、are modelled. The following alphabetical list gives the sub-clause of each definition. acoustic modifier application captured primitive coordinate coordinator form primitive geometric primitive graphics input device media engine modeller modifier primitive operator presentation primitive primitive s
23、tructure renderer router scene structural modifier structured primitive temporal extent tracer primitive visual modifier wrapper primitive 3.264. I 3.2.1.5 3.2.6.2 3.2.5 3.2.1 I 3.2.6.1 3.2.6. I. I 3.2.8 3.2.7 3.2.3 3.2.1 3.2.6.4 3.2.14 3.2.4 3.2.6 3.2.10 3.2.2 3.2.12 3.2.9 3.2.6.4.2 3.2.6.3 3.2.13
24、3.2.6.6 3.2.6.4.3 3.2.6.5 3 ISO/IEC 14478-4:1998(E) 0 ISO/IEC 4 Symbols and abbreviations CGRM: CSG: GKS: IEC: ISO: MPEG: MRI: MSS: PHIGS: PREMO: VRML: nD: 2D: 3D: Computer Graphics Reference Model. Constructive Solid Geometry Graphical Kernel System. International Electrotechnical Commission. Inter
25、national Organization for Standardization. Moving Picture Experts Group. Modelling, Rendering and Interaction Multimedia Systems Services Programmers Hierarchical Interactive Graphics System. Presentation Environment for Multimedia Objects. Virtual Reality Modeling Language. Multi-dimensional. Two-d
26、imensional. Three-dimensional. 5 Conformance A conforming implementation of the PREMO Modellin, 0 Rendering and Interaction Component shall comply with the general conformance rules defined in clause 5 of ISOUEC 14478-l and the component specification in clause 16. 6 Overview of the Modelling, Rende
27、ring and Interaction Component. 6.1 Introduction This clause presents an overview of the modelling, rendering, and interaction component (Part 4) of PREMO. It summarises the concepts defined in the document, and explains how these concepts contribute to the goals set out in the Introduction. More de
28、- tailed descriptions of the concepts used in the overview are given in subsequent clauses. This part of ISO/IEC 14478 also makes extensive use of facilities provided by PREMO parts l-3, in particular the device and stream concepts introduced in ISO/IEC 14478-3. A summary of these dependencies is in
29、cluded in this clause. 6.2 Overview The model underlying this part of ISO/IEC 14478 is that a multimedia system consists of modellers, renderers, and other devices (some media specific) linked together via streams that carry data of a particular format. These concepts of stream and device are those
30、defined in ISO/IEC 14478-3. A device consists of a processing facility, together with a number of ports through which it can accept input and produce output, using a format defined by the port. Figure I shows a high-level view of a (simplified) ex- ample system in which a graphical user interface is
31、 used to control parameters of an audio-visual presentation system. Rectangles on the sides of devices represent ports, and the thick lines between such ports represent media flow via streams. Thin lines rep- resent other forms of interaction, for example operation invocation. See also Annex B for a
32、 table defining the symbols used in the figure. The system in Figure I consists of: 4 0 ISO/IEC ISO/IEC 14478-4:1998(E) from application 7 / graphics graphics engine renderer / L / video engine c / Figure 1 - An audio/visual system - two modellers, one for audio data and one for graphical data, that
33、 might be used to construct and edit primitives via an interface to the application specific to the needs of each modeller; - a video engine, accepting a stream of video data from the application and constructing a stream of information in some video format; - a scene, which encapsulates primitives
34、produced by the two modellers and which mediates access to the collection of primitives by both the modellers and the associated renderers; - an audio engine, that takes primitives from the scene and converts into a data format that can be used to drive an audio- specific device; - a graphics engine
35、 (acting as a mixer or composition tool) uses the video output from the video renderer and primitives from the scene to construct a further stream of primitives, integrating the two sets of source data within some appropriate visual representation. The primitives produced by the engine may be some s
36、ubset suitable for input to a specific renderer; - two renderers, one for audio and one for graphics, that convert a stream of primitives into a form that can be processed in the context beyond the MRI network (in this case, presented to the end user of the application). The figure shows just one wa
37、y in which such a system might be implemented. A different implementation may collapse the three engines into a single device, if it has access to a media engine that can take both graphical and audio primitives as input and that can generate the corresponding output streams. Another implementation
38、may decompose the graphics engine into, for example, a number of components that manage specific functionalities such as viewing or clipping. Finally, a high-performance implemen- tation might collapse all components into a single device. Key components of this part are derived from the object types
39、 defined in ISO/IEC 14478-3, in particular the property inquiry and constraint facilities. These types and facilities may be used by the factory mechanism described in ISO/IEC 14478-2 to produce ob.jects that meet certain requirements, and by the negotiation and QoS mechanisms for establishing and m
40、aintaining a network of ob.jects that satisfies specific properties. As a result, many of the object types defined in this part have an associated list of properties for use in creation and negotiation. For example, modellers and renderers are derived (indirectly) from the VirtuaUh sice type of ISO/
41、IEC 14478-3, and thus inherit the Property Inquiry services. Each renderer and modeller has a collection of prop- erties that characterise its capabilities in terms of its inputs, outputs and quality of service. An application using the facilities of this part can request creation of a renderer from
42、 a renderer factory by invoking the create-object operation using the type ren- derer as the name of the object type and passing a structure containing the required capabilities. Alternatively, an application that is aware that the rendering interface it requires is defined by a specific subtype of
43、the renderer can request the factory to produce a renderer of that specific type. 5 ISO/IEC 14478-4:1998(E) 0 ISO/IEC from application Figure 2 - MRI network including interaction handling For simplicity, Figure I illustrates devices used in presentation only. The same approach of using specialised
44、virtual devices con- nected by data streams is employed for handling input and interaction. Figure 2 extends the example with a simple framework for input handling. This introduces two new devices, and a new information flow between two renderers, shown in the outlined regions of the figure. - The m
45、ouse is an example of an InputDevice that can provide primitives for processing elsewhere in the network, either via a stream (as shown) or through a procedural interface or callback mechanism. - A Router can be incorporated to allow a data stream to be sent to specific devices depending on some int
46、ernal state. The Router device achieves this by also subtyping from the Controller object defined in ISO/IEC 14478-2. - Although Eqine objects primarily operate on streams of primitives intended for presentation, as the example shows, an engine may also have ports that are used to receive (and in th
47、e case of the graphics engine, to transmit) primitives used to carry data about input. Figure I and Figure 2 focus on the main streams and virtual devices involved in a simple MRI network. In addition to these, ISO/ IEC 14478-3 provides object types for establishing and controlling a collection of s
48、treams and devices. These types are called VirtunlConnectiorl and Group, respectively. An instance of VirtualConnection is an object that represents an abstract view of media transport between devices, allows control over aspects of the connection, and is responsible for negotiating the connection i
49、n terms of formats and quality of service con- siderations etc. Several kinds of virtual connections are possible, depending on whether the devices have compatible ports, and on whether a particular connection is local or networked. General examples of these are given in Annex D of ISO/IEC 14478-3. If the ports of two devices are not compatible, or the devices are in different parts of a distributed environment, connection adap- tars will be employed. These adapters are an implementation concept, not visible to the application, and are not defined as an object type in the profile of I
